Unification-typed electrode assembly and secondary battery using the same

ABSTRACT

Disclosed herein is an integrated electrode assembly including a cathode, an anode, and a separation layer integrated between the cathode and the anode. The separation layer includes 3 phases including a liquid-phase component containing an ionic salt, which partially flows from the separation layer into the cathode and the anode during preparation of the integrated electrode assembly to increase ionic conductivity of the cathode and the anode, a solid-phase component supporting the separation layer between the cathode and the anode, and a polymer matrix having affinity for the liquid-phase component and providing binding force with the cathode and the anode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/KR2012/001560 filed on Mar. 2, 2012, which claims the benefit ofPatent Application No. 10-2011-0018757 filed on Mar. 3, 2011. The entirecontents of all of the above applications are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to an integrated electrode assembly and asecondary battery using the same and more particularly to an integratedelectrode assembly including a cathode, an anode, and a separation layerintegrated between the cathode and the anode, the separation layerincluding 3 phases including a liquid-phase component containing anionic salt, which partially flows from the separation layer into theelectrodes (i.e., the cathode and the anode) during preparation of theintegrated electrode assembly to greatly improve wetting properties ofthe electrodes and to increase ionic conductivity of the electrodes, asolid-phase component supporting the separation layer between thecathode and the anode, and a polymer matrix having affinity for theliquid-phase component and providing binding force with the cathode andthe anode.

BACKGROUND ART

Increasing price of energy sources due to depletion of fossil fuels andan increased interest in environmental pollution have brought aboutincreased demand for environmentally friendly alternative energy sourcesas an indispensable element for future life. Studies on various powergeneration technologies such as nuclear, solar, wind, and tidal powergeneration technologies have continued to be conducted and power storagedevices for more efficient use of such generated energy also continue tobe of great interest. Secondary batteries have been used as such powerstorage devices. Among secondary batteries, lithium secondary batterieshave begun to be used for mobile devices and, along with increasingdemand for reduced weight and high voltage and capacity, recently, useof lithium secondary batteries has been significantly extended toelectric vehicles, hybrid electric vehicles, and auxiliary power sourcesbased upon smart grid.

However, numerous challenges, which have yet to be addressed, remainbefore lithium secondary batteries can be used as large-capacity powersources. One important challenge is to improve energy density andincrease safety. Another important challenge is to reduce process timeand to achieve uniform wetting for large-area electrodes. Manyresearchers have conducted intensive studies on materials that cansatisfy low cost requirements while increasing energy density and havealso put effort into studies on materials for improving safety.

Ni-based or Mn-based materials having higher capacity than LiCoO₂, whichhas been conventionally used, are typical examples of materials beingstudied for energy density improvement. Materials that are based on Lialloying reactions with Si or Sn rather than based on intercalationreactions are typical examples of materials for anodes being studied asalternatives to conventional graphite-based materials.

A stable olivine-based cathode active material such as LiFePO₄, acathode active material such as Li₄Ti₅O₁₂, or the like have been studiedto improve safety. However, such materials for safety improvementinherently have a low energy density and do not fundamentally solvesafety problems associated with the structure of lithium secondarybatteries.

Secondary battery safety may be largely divided into internal safety andexternal safety and may further be divided into electrical safety,impact safety, and thermal safety. Occurrence of these safety problemscommonly entails temperature increase, which necessarily results incontraction of a stretched separator that is generally used.

Although many researchers have suggested all-solid-state batteries toresolve this safety issue, all-solid-state batteries have a lot ofproblems in replacing batteries available on the market.

First, currently used electrode active materials are in a solid state.Thus, when a solid electrolyte or a polymer electrolyte is used, thesurface area of the electrolyte in contact with the active material forlithium ion movement is significantly reduced. Therefore, the ionicconductivity is very low even when the solid or polymer electrolyte hasa conductivity of 10⁻⁵ s/cm, similar to the current liquid electrolyte.Second, the ionic conductivity at the solid-solid interface or thesolid-polymer interface should be much lower for the same reason. Third,even when a solid electrolyte with high conductivity is used, the ionicconductivity is still very low due to a polymer binder that should beemployed to provide binding force that is essential to batteryformation. Fourth, to form a battery, not only the separation layerneeds to have ionic conductivity but the cathode and anode activematerials also need to employ materials for ionic conductivityimprovement to increase ionic conductivity of the electrodes. However,if a solid electrolyte or a polymer electrolyte is included as anelectrode component, the capacity is reduced.

Thus, there is a great need to provide a battery structure that preventsshort-circuiting due to separator contraction and provides excellentbattery performance.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the above andother technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies and variousexperiments, the present inventors have found that an integratedelectrode assembly, which includes a separation layer including threephases including a liquid-phase component containing an ionic salt, asolid-phase component supporting the separation layer between a cathodeand an anode, and a polymer matrix incorporating the liquid-phasecomponent and the solid-phase component therein, preventsshort-circuiting due to separator contraction, greatly improves wettingproperties of the electrodes, and increases ionic conductivity. Thepresent invention has been completed based on this finding.

Technical Solution

Therefore, an integrated electrode assembly in accordance with thepresent invention includes a cathode, an anode, and a separation layerintegrated between the cathode and the anode, the separation layerincluding 3 phases including a liquid-phase component containing anionic salt, the liquid-phase component partially flowing from theseparation layer into the cathode and the anode during preparation ofthe integrated electrode assembly to greatly improve wetting propertiesof the cathode and the anode and to increase ionic conductivity of thecathode and the anode, a solid-phase component supporting the separationlayer between the cathode and the anode, and a polymer matrix havingaffinity for the liquid-phase component and providing binding force withthe cathode and the anode.

Experiments conducted by the present inventors showed that the internalrisk of the secondary battery is highest when the secondary battery isin a charged state with increased energy and, when the secondary batteryis in a charged state, short-circuiting may be caused by separatorcontraction or the like in four situations: (1) where a charged cathodeand a charged anode contact each other, (2) where a charged cathode andan anode current collector contact each other, (3) where an anodecurrent collector and a cathode current collector contact each other,and (4) where a cathode current collector and a charged anode contacteach other.

Experiments conducted in all of the situations with charged electrodesin a dry room showed that most serious thermal runaway occurred uponcontact between a charged anode and a cathode current collector,contrary to what was expected. Through intensive study, we found thatsuch thermal runaway was caused by, for example, a rapid exothermicreaction of 4Al+3O₂→2Al₂O₃ at an Al foil which serves as a cathodecurrent collector. The shapes of Al foils were hard to identify in alloccurrences of battery explosion.

Although the experiments showed that thermal runaway occurred only whena charged anode and a cathode current collector contact each other, itcannot be concluded that the other three situations are safe. Inbatteries, any contact between portions of a cathode and an anode isrisky.

On the other hand, the integrated electrode assembly according to thepresent invention has excellent high-temperature safety since a polymermatrix and a solid-phase component do not contract at high temperature,preventing the occurrence of mishaps such as explosion that occurred inthe above experiments.

In addition, it is possible to increase ionic conductivity of theelectrodes (i.e., the anode and cathode), thereby improving batteryperformance, since the liquid-phase component flows into and impregnatesthe electrodes in an electrode assembly preparation process, forexample, in a lamination process. Further, since the electrodes areuniformly wetted by electrolyte, it is possible to minimize electrodedegradation caused by non-uniform permeation of electrolyte, which isthe most serious problem associated with large-area electrodes.Accordingly, the electrolyte state of the electrode assembly of thepresent invention may be defined such that a partial liquid-phasecomponent derived from the separation layer is included or incorporatedin the electrodes. Here, the amount of the liquid-phase componentderived from the separation layer which is included or incorporated inthe electrodes is not particularly limited. For example, the amount ofthe liquid-phase component included or incorporated in the electrodesmay be 10 to 90% based on the total amount of the liquid-phase componentincluded in the electrode assembly.

The weight ratio of the liquid-phase component to the polymer matrix ispreferably from 3:7 to 9:1. When the content of the liquid-phasecomponent is excessively low, an insufficient amount of liquid-phasecomponent may flow into the electrodes, failing to increase ionicconductivity of the electrodes. Conversely, when the content of theliquid-phase component is excessively high, an excess of liquid-phasecomponent may negatively affect the process. Therefore, the weight ratioof the liquid-phase component to the polymer matrix is more preferablyfrom 5:5 to 8:2.

The polymer matrix may be in the form of a mixture of linear polymer andcross-linked polymer. In this case, the weight ratio of the linearpolymer to the cross-linked polymer is preferably 1:9 to 8:2 althoughthe weight ratio of the linear polymer to the cross-linked polymer isnot particularly limited so long as a viscoelastic structure can beformed. An excessively low or high content of linear polymer isundesirable since this reduces elasticity and degrades mechanicalproperties, reducing impregnation performance of the liquid-phasecomponent.

Although the types of the polymers that constitute the polymer matrix inthe present invention are not particularly limited, preferred examplesof the polymers include at least one selected from the group consistingof an oxide-based non-cross-linked polymer, a polar non-cross-linkedpolymer, and a cross-linked polymer having a three-dimensional networkstructure.

More preferably, the polymer matrix includes both an oxide-basednon-cross-linked polymer and a polar non-cross-linked polymer.

Non-limiting examples of the oxide-based non-cross-linked polymerinclude at least one selected from the group consisting of poly(ethyleneoxide), poly(propylene oxide), poly(oxymethylene), andpoly(dimethylsiloxane).

Non-limiting examples of the polar non-cross-linked polymer include atleast one selected from the group consisting of polyacrylonitrile,poly(methyl methacrylate), poly(vinyl chloride), poly(vinylidenefluoride), poly(vinylidenefluoride-co-hexafluoropropylene),poly(ethylene imine), and poly(p-phenylene terephthalamide).

The cross-linked polymer included in the polymer matrix in the presentinvention may include a polymer obtained from monomers having at leasttwo functional groups or a copolymer obtained from monomers having atleast two functional groups and polar monomers having one functionalgroup.

Although the type of the monomers having at least two functional groupsis not particularly limited, the monomers preferably include at leastone selected from the group consisting of trimethylolpropane ethoxylatetriacrylate, polyethylene glycol dimethacrylate, polyethylene glycoldiacrylate, divinylbenzene, polyester dimethacrylate, divinyl ether,trimethylolpropane, trimethylolpropane trimethacrylate, and ethoxylatedbis phenol A dimethacrylate.

Although the type of the polar monomers having one functional group isnot particularly limited, the polar monomers preferably include at leastone selected from the group consisting of methyl methacrylate, ethylmethacrylate, butyl methacrylate, methyl acrylate, butyl acrylate,ethylene glycol methyl ether acrylate, ethylene glycol methyl ethermethacrylate, acrylonitrile, vinyl acetate, vinyl chloride, and vinylfluoride.

The separation layer preferably includes 2 to 80% by weight of thesolid-phase component based on the weight of the polymer matrix. Whenthe separation layer includes less than 2% by weight of the solid-phasecomponent based on the weight of the polymer matrix, disadvantageously,the effects of supporting the separation layer, for example, mechanicalstrength of the separation layer, may be insufficient. When theseparation layer includes more than 80% by weight of the solid-phasecomponent based on the weight of the polymer matrix, disadvantageously,ionic conductivity may be decreased, reducing battery performance, andbrittleness may occur during charge/discharge due to high rigidity.Therefore, the separation layer more preferably includes 20 to 50% byweight of the solid-phase component based on the weight of the polymermatrix.

Although the composition of the liquid-phase component is notparticularly limited so long as the liquid-phase component can partiallyflow into the electrodes, increasing ionic conductivity of theelectrodes, the liquid-phase component is preferably an electrolytecontaining an ionic salt.

For example, the ionic salt may include, but is not limited to, alithium salt and the lithium salt may include, but is not limited to, atleast one selected from the group consisting of LiCl, LiBr, LiI, LiClO₄,LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄,CH₃SO₃Li, (CF₃SO₂)₂NLi, chloroborane lithium, lower aliphatic carboxylicacid lithium, and lithium tetraphenylborate.

The electrolyte may include, but is not limited to, at least oneselected from the group consisting of ethylene carbonate, propylenecarbonate, butylene carbonate, vinylene carbonate, diethyl carbonate,dimethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone,sulfolane, methyl acetate, and methyl propionate.

The solid-phase component is a solid compound that is not reactive withlithium ions and preferably includes solid-phase particles having a meanparticle diameter of 10 nm to 5 μm. When the mean particle diameter ofthe solid-phase component is too small, disadvantageously, thesolid-phase component may be present in the form of clusters, resultingin a failure to properly support the separation layer. Conversely, whenthe mean particle diameter of the solid-phase component is too great,disadvantageously, the thickness of the separation layer may be greaterthan needed. Therefore, the mean particle diameter of the solid-phasecomponent is more preferably 50 nm to 200 nm.

In a preferred embodiment, the solid compound may include, but is notlimited to, at least one selected from the group consisting of an oxide,a nitride, and a carbide that are not reactive with lithium ions.

Preferred examples of the oxide that is not reactive with lithium ionsmay include, without being limited to, at least one selected from thegroup consisting of MgO, TiO₂ (rutile) and Al₂O₃.

In the electrode assembly of the present invention, the cathode may beproduced, for example, by adding a cathode mix including a cathodeactive material to a solvent such as NMP to prepare a slurry andapplying the slurry to a cathode current collector, followed by drying.Optionally, the cathode mix may further include a binder, a conductivematerial, a filler, a viscosity controller, and an adhesion promoter.

The cathode current collector is generally manufactured to a thicknessof 3 to 500 μm. Any cathode current collector may be used withoutparticular limitation so long as high conductivity is provided withoutcausing chemical changes in the battery. Examples of the cathode currentcollector include stainless steel, aluminum, nickel, titanium, sinteredcarbon, or aluminum or stainless steel surface-treated with carbon,nickel, titanium or silver. Similar to the anode current collector, thecathode current collector may include fine irregularities on the surfacethereof so as to enhance adhesion to the cathode active material. Inaddition, the cathode current collector may be used in various formssuch as a film, a sheet, a foil, a net, a porous structure, a foam and anonwoven fabric.

The cathode active material is a lithium transition metal oxideincluding two or more transition metals as a substance that causeselectrochemical reaction, and examples thereof include, but are notlimited to, layered compounds such as lithium cobalt oxide (LiCoO₂) orlithium nickel oxide (LiNiO₂) substituted by one or more transitionmetals, lithium manganese oxide substituted by one or more transitionmetals, lithium nickel-based oxides represented by the formulaLiNi_(1-y)M_(y)O₂ (in which M=Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga,the lithium nickel-based oxide including at least one of the elements,and 0.01≦y≦0.7), lithium nickel cobalt manganese composite oxidesrepresented by the formulaLi_(1+z)Ni_(b)Mn_(e)Co_(1-(b+c+d))M_(d)O_((2-e))A_(e) such asLi_(1+z)Ni_(1/3)CO_(1/3)Mn_(1/3)O₂ or Li_(1+z)Ni_(0.4)Mn_(0.4)CO_(0.2)O₂(in which −0.5≦z≦0.5, 0.1≦b≦0.8, 0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, b+c+d<1,M=Al, Mg, Cr, Ti, Si or Y, A=F, P or Cl), and olivine-based lithiummetal phosphates represented by the formulaLi_(1+x)M_(1-y)M′_(y)PO_(4-z)X_(z) (in which M=a transition metal,preferably, Fe, Mn, Co or Ni, M′=Al, Mg or Ti, X═F, S or N, 0.5≦x≦0.5,0≦y≦0.5, and 0≦z≦0.1).

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), cellulose, polyvinyl alcohol,carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymers(EPDM), sulfonated EPDM, styrene butadiene rubbers, fluoro-rubbers,various copolymers, and polymer-saponified polyvinyl alcohols.

Any conductive material may be used without particular limitation solong as suitable conductivity is provided without causing chemicalchanges in the battery. Examples of the conductive material includegraphite, carbon blacks such as acetylene black. Ketjen black, channelblack, furnace black, lamp black and thermal black, conductive fiberssuch as carbon fibers and metallic fibers, metallic powders such ascarbon fluoride, aluminum and nickel powders, conductive whiskers suchas zinc oxide and potassium titanate whiskers, conductive metal oxidessuch as titanium oxide, and polyphenylene derivatives. Specific examplesof commercially available conductive materials include various acetyleneblack products (available from Chevron Chemical company, Denka SingaporePrivate Limited and Gulf Oil company), Ketjen Black EC series (availablefrom Armak company), Vulcan XC-72 (available from Cabot company) andSuper P (available from Timcal company).

Any filler may be used without particular limitation so long as thefiller is a fibrous material that does not cause chemical changes in thebattery. Examples of the filler include olefin-based polymers such aspolyethylene and polypropylene and fibrous materials such as glassfibers and carbon fibers.

The viscosity controller is a component that controls the viscosity ofthe electrode mix to facilitate mixing of the electrode mix andapplication of the same to a current collector, and may be added in anamount of up to 30% by weight, based on the total weight of the anodemix. Examples of the viscosity controller include, but are not limitedto, carboxymethyl cellulose and polyvinylidene fluoride. In some cases,the afore-mentioned solvent may also act as the viscosity controller.

The adhesion promoter is an auxiliary ingredient that is added toimprove adhesion of an active material to a current collector. Theadhesion promoter may be added in an amount of not more than 10% byweight, relative to the binder. Examples of the adhesion promoterinclude oxalic acid, adipic acid, formic acid, and acrylic acidderivatives and itaconic acid derivatives.

The anode may be produced, for example, by adding an anode mix includingan anode active material to a solvent such as NMP to prepare a slurryand applying the slurry to an anode current collector, followed bydrying. Optionally, the anode mix may further include other componentssuch as a binder, a conductive material, a filler, a viscositycontroller, and an adhesion promoter, which are described above inassociation with the configuration of the cathode.

The anode current collector is generally fabricated to a thickness of 3to 500 μm. Any anode current collector may be used without particularlimitation so long as suitable conductivity is provided without causingchemical changes in the battery.

Examples of the anode current collector include copper, stainless steel,aluminum, nickel, titanium, sintered carbon, copper or stainless steelsurface-treated with carbon, nickel, titanium or silver, andaluminum-cadmium alloys. The anode current collector may include fineirregularities on the surface thereof so as to enhance adhesion of anodeactive materials. In addition, the current collector may be provided invarious forms such as a film, a sheet, a foil, a net, a porousstructure, a foam and a nonwoven fabric.

Examples of the anode active material include carbon-graphite materialssuch as natural graphite, artificial graphite, expanded graphite, carbonfiber, non-graphitizing carbon, carbon black, carbon nanotubes,fullerene, and activated carbon, metals alloyable with lithium such asAl, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pt, and Ti, compounds includingthese elements, complexes of the metals or the compounds thereof withthe carbon-graphite materials, and lithium-containing nitrides. Amongthese materials, carbon-based active materials, tin-based activematerials, silicon-based active materials, or silicon-carbon-basedactive materials are more preferable and may be used singly or incombination of at least two thereof.

The present invention also provides a method for preparing theintegrated electrode assembly described above.

The method for preparing the integrated electrode assembly includes thesteps of:

(1) homogenizing a linear polymer, monomers for a cross-linked polymer,a liquid-phase component including an ionic salt, a solid-phasecomponent, and a polymerization initiator into a mixture;

(2) coating the mixture on one electrode;

(3) inducing polymerization reaction through UV irradiation or heatingto form a separation layer; and

(4) placing a counter electrode on the separation layer, followed bypressing.

A conventional method, in which a mold is prepared to form a spacebetween a cathode and an anode and a polymer-monomer mixture isintroduced into the space, followed by polymerization, has many processdifficulties.

On the other hand, the above method in which the mixture is coated onone electrode, followed by polymerization, can simplify the process. Theabove method is also suitable for battery performance improvement since,during pressing in step (4), the liquid-phase component of theseparation layer partially flows into the electrodes and impregnates theelectrodes, improving ionic conductivity of the electrodes.

In step (1), the linear polymer is mixed in the form of a polymer ratherthan in the form of monomers, such that the linear polymer partiallypermeates into a cross-linked polymer gel (g) during polymerization intoa cross-linked polymer in step (3) to form a physical connectionstructure. This structure may be more suitable for preparation of aseparation layer having high structural stability and viscoelasticity.The size of the part of the linear polymer that permeates into thecross-linked polymer gel is preferably less than 50% and more preferably5 to 45% based on the total size of the linear polymer.

The present invention also provides a lithium secondary batteryincluding the integrated electrode assembly. The lithium secondarybattery may include the integrated electrode assembly and, optionally, alithium salt-containing non-aqueous electrolyte. In a preferredembodiment, the lithium secondary battery may contain no or only a smallamount of lithium salt-containing non-aqueous electrolyte.

This is possible since pressing in step (4) causes the liquid-phasecomponent of the separation layer to partially flow into the electrodes,impregnating the electrodes. Taking into consideration that electrolyteimpregnation is a bottleneck in the battery fabrication process, thepresent invention can provide a secondary battery with high processefficiency.

The present invention also provides a middle or large-sized batterymodule including the lithium secondary battery as a unit cell and abattery pack including the battery module.

The battery pack may be used in various middle or large-sized devices,especially those requiring high-temperature safety and high rateproperties. Examples of the middle or large-sized devices, for which thebattery pack may be used as a power source, include, but are not limitedto, power tools that are powered by electrical motors, electric vehicles(EVs) including hybrid electric vehicles (HEVs) and plug-in hybridelectric vehicles (PHEVs), electric two-wheeled vehicles includingelectric bikes (E-bikes) and electric scooters (E-scooters), electricgolf carts, and power storage systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic cross-sectional view of an integrated electrodeassembly according to one embodiment of the present invention;

FIG. 2 is a schematic enlarged inside view of a 3-phase separation layeraccording to one embodiment of the present invention;

FIG. 3 is a graph showing measurement results of tensile strengthaccording to Example 1 of the present invention; and

FIG. 4 is a graph showing charge/discharge results according to Example2 of the present invention.

BEST MODE

Now, the present invention will be described with reference to thedrawings, which illustrate embodiments of the present invention.However, it should be noted that the description of the embodiments isto provide better understanding of the present invention withoutlimiting the scope of the invention.

FIG. 1 is a schematic cross-sectional view of an integrated electrodeassembly according to one embodiment of the present invention and FIG. 2is a schematic enlarged inside view of a 3-phase separation layeraccording to one embodiment of the present invention.

As shown in FIGS. 1 and 2, the electrode assembly 100 according to oneembodiment of the present invention includes a cathode 110, an anode120, and a 3-phase separation layer 130. The cathode 110 has a structurein which cathode mixes 112 and 113 are coated on both sides of a cathodecurrent collector 111, the anode 120 has a structure in which anodemixes 122 and 123 are coated on both sides of an anode current collector121, and the 3-phase separation layer 130 is positioned between thecathode 110 and the anode 120.

The 3-phase separation layer 130 includes a solid-phase component 131, aliquid-phase component 132, and a polymer matrix in which linearpolymers 133 and cross-linked polymers 134 form a viscoelastic structurewith the solid-phase component 131 and the liquid-phase component 132being incorporated in the polymer matrix.

Such an integrated electrode assembly has excellent high-temperaturesafety since the polymer matrix and the solid-phase component do notcontract at high temperature, preventing the occurrence of mishaps suchas explosion.

In addition, it is possible to increase ionic conductivity of theelectrodes 110 and 120, improving battery performance, since theliquid-phase component 132 flows into the electrodes 110 and 120 in anarrow direction shown in FIG. 2, impregnating the electrodes 110 and120, in an electrode assembly preparation process, for example, in alamination process. Further, since the electrodes 110 and 120 areuniformly wetted by electrolyte, it is possible to minimize degradationof the electrodes 110 and 120 caused by non-uniform permeation ofelectrolyte, which is the most serious problem associated withlarge-area electrodes.

Hereinafter, the present invention will be described in more detail withreference to the following examples. However, it should be noted thatthe following examples are provided only to illustrate the presentinvention and the scope of the present invention is not limited thereto.

Example 1

A mixture of an organic electrolyte of 1M LiPF₆ in EC:DEC (1:1), PEO,PEGDMA, and Al₂O₃ in a weight ratio of 76:15.4:6.6:2 was prepared andbenzoin was added as a UV initiator in an amount of 3% by weightrelative to PEGDMA to prepare a precursor of a 3-phase separation layer.The precursor was coated on a glass plate, which was then irradiatedwith ultraviolet light for 1 minute to produce a 3-phase separationlayer through photopolymerization.

Comparative Example 1

A mixture of an organic electrolyte of 1M LiPF₆ in EC:DEC (1:1),PVdF-HFPPVdF-HFP, and Al₂O₃ in a weight ratio of 76:22:2 was prepared,acetone was added as a solvent in an amount of 20% by weight relative tothe total weight, and the mixture was homogenized. The mixture was thencasted onto a glass plate and acetone was evaporated for 10 hours underan argon gas atmosphere in a glove box to produce a solid electrolytemembrane.

Experimental Example 1

Ionic conductivity and tensile strength were measured for each of the3-phase separation layer of Example 1 and the solid electrolyte membraneof Comparative Example 1.

As a result, Example 1 and Comparative Example 1 exhibited similarlevels of ionic conductivity of 1.2 mS/cm and 1.7 mS/cm. On the otherhand, as can be seen from FIG. 3, the measurement results of tensilestrength showed that the tensile strength of the 3-phase separationlayer of Example 1 having a viscoelastic structure was greatly improvedover that of the solid electrolyte membrane of Comparative Example 1.

Example 2

Graphite, PVdF and carbon black were added to N-methyl-pyrrolidinone toprepare a slurry and the slurry was applied to a Cu foil. Theslurry-applied Cu foil was then dried for 2 hours at about 130° C. toprepare an anode. In addition, Li(NiMnCo)O₂/LiMnO₂, PVdF and carbonblack were added to N-methyl-pyrrolidinone to prepare a slurry and theslurry was applied to a Cu foil. The slurry-applied Cu foil was thendried for 2 hours at about 130° C. to prepare a cathode.

The 3-phase separation layer precursor of Example 1 was coated on theanode, which was then irradiated with ultraviolet light for 1 minute toproduce a 3-phase separation layer through photopolymerization.

The cathode was placed on the anode coated with the 3-phase separationlayer, followed by lamination to prepare an integrated electrodeassembly. The integrated electrode assembly was then inserted into apouch without an impregnation process to fabricate a secondary battery.

Comparative Example 2

A polyolefin-based separator was placed between the anode and cathode ofExample 2, which was then inserted into a pouch. An electrolyte of 1MLiPF₆ in EC:DEC (1:1) was then introduced into the pouch to fabricate asecondary battery.

Experimental Example 2

The secondary batteries of Example 2 and Comparative Example 2 werecharged in a constant current (CC) mode at a current density of 0.1 C to4.2 V and were then maintained in a constant voltage (CV) mode at 4.2 Vand charging was completed when current density reached 0.05 C. Duringdischarge, the secondary batteries were discharged in a CC mode at acurrent density of 0.1 C to 2.5V. Then, charge/discharge was repeated 50times under the same conditions as above. Results are shown in FIG. 4.

It can be seen from FIG. 4 that the secondary battery of Example 2including the integrated electrode assembly employing the 3-phaseseparation layer exhibits charge/discharge properties similar to thesecondary battery of Comparative Example 2 employing the liquidelectrolyte and the separator although the secondary battery of Example2 has not been subjected to an impregnation process. Therefore, thesecondary battery of Example 2 is free from the problem of poorimpregnation of electrolyte which has been pointed out as a problem ofthe solid electrolyte.

INDUSTRIAL APPLICABILITY

As is apparent from the above description, an integrated electrodeassembly according to the present invention has an advantage in that itis possible to prevent short-circuiting due to separator contraction. Inaddition, electrolyte is impregnated into the electrodes duringpreparation of the electrode assembly. Therefore, it is possible togreatly alleviate the problem of increased process time and the problemof non-uniform electrodes associated with wetting. It is also possibleto improve ionic conductivity of the electrodes.

It will be apparent to those skilled in the art that variousapplications and modifications can be made based on the abovedescription without departing from the scope of the invention.

The invention claimed is:
 1. An integrated electrode assembly comprisinga cathode, an anode, and a separation layer integrated between thecathode and the anode, the separation layer comprising 3 phasescomprising: a liquid-phase component containing an ionic salt, theliquid-phase component partially flowing from the separation layer intothe cathode and the anode of the integrated electrode assembly andimpregnates these electrodes to increase ionic conductivity of thecathode and the anode; a solid-phase component supporting the separationlayer between the cathode and the anode; and a polymer matrix havingaffinity for the liquid-phase component and providing binding force withthe cathode and the anode, wherein the polymer matrix is in the form ofa mixture of a linear polymer and a cross-linked polymer, and the weightratio of the linear polymer to the cross-linked polymer is 1:9 to 8:2,wherein the mixture of the linear polymer and the cross-linked polymerforms a viscoelastic structure, wherein the liquid-phase component is anelectrolyte containing the ionic salt, wherein a weight ratio of theliquid-phase component to the polymer matrix is from 5:5 to 8:2, andwherein the separation layer is in the form of a single layer structurein which the solid-phase component and the liquid-phase component areincorporated in the polymer matrix, wherein the linear polymer, thecross-linked polymer, the liquid-phase component and the solid-phasecomponent are homogenized in the separation layer, wherein a firstsurface of the separation layer forms a layer directly on a surface ofthe cathode and a second surface of the separation layer forms a layerdirectly on a surface of the anode, and wherein the linear polymerpartially permeates into the cross-linked polymer, and a size of thepart of the linear polymer that permeates into the cross-linked polymeris 5 to 45% based on the total size of the linear polymer.
 2. Theintegrated electrode assembly according to claim 1, wherein the polymermatrix comprises the cross-linked polymer having a three-dimensionalnetwork structure, and at least one selected from the group consistingof an oxide-based non-cross-linked polymer and a polar non-cross-linkedpolymer as the linear polymer.
 3. The integrated electrode assemblyaccording to claim 2, wherein the polymer matrix comprises anoxide-based non-cross-linked polymer, wherein the oxide-basednon-cross-linked polymer comprises at least one selected from the groupconsisting of poly(ethylene oxide), poly(propylene oxide),poly(oxymethylene), and poly(dimethylsiloxane).
 4. The integratedelectrode assembly according to claim 2, wherein the polymer matrixcomprises a polar non-cross-linked polymer, wherein the polarnon-cross-linked polymer comprises at least one selected from the groupconsisting of polyacrylonitrile, poly(methyl methacrylate), poly(vinylchloride), poly(vinylidene fluoride),poly(vinylidenefluoride-co-hexafluoropropylene), poly(ethylene imine),and poly(p-phenylene terephthalamide).
 5. The integrated electrodeassembly according to claim 2, wherein the cross-linked polymercomprises a polymer having at least two monomers or a copolymer havingat least two monomers.
 6. The integrated electrode assembly according toclaim 5, wherein the cross-linked polymer comprises a polymer having atleast two monomers, wherein the at least two monomers comprise at leastone selected from the group consisting of trimethylolpropane ethoxylatetriacrylate, polyethylene glycol dimethacrylate, polyethylene glycoldiacrylate, divinylbenzene, polyester dimethacrylate, divinyl ether,trimethylolpropane, trimethylolpropane trimethacrylate, and ethoxylatedbis phenol A dimethacrylate.
 7. The integrated electrode assemblyaccording to claim 5, wherein the cross-linked polymer comprises acopolymer obtained from monomers having at least two functional groupsand polar monomers having one functional group, wherein the polarmonomers having one functional group comprise at least one selected fromthe group consisting of methyl methacrylate, ethyl methacrylate, butylmethacrylate, methyl acrylate, butyl acrylate, ethylene glycol methylether acrylate, ethylene glycol methyl ether methacrylate,acrylonitrile, vinyl acetate, vinyl chloride, and vinyl fluoride.
 8. Theintegrated electrode assembly according to claim 1, wherein theseparation layer comprises 2 to 80% by weight of the solid-phasecomponent based on the weight of the polymer matrix.
 9. The integratedelectrode assembly according to claim 1, wherein the ionic salt is alithium salt.
 10. The integrated electrode assembly according to claim9, wherein the lithium salt comprises at least one selected from thegroup consisting of LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆,LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, (CF₃SO₂)₂NLi,chloroborane lithium, lower aliphatic carboxylic acid lithium, andlithium tetraphenylborate.
 11. The integrated electrode assemblyaccording to claim 1, wherein the electrolyte comprises at least oneselected from the group consisting of ethylene carbonate, propylenecarbonate, butylene carbonate, vinylene carbonate, diethyl carbonate,dimethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone,sulfolane, methyl acetate, and methyl propionate.
 12. The integratedelectrode assembly according to claim 1, wherein the solid-phasecomponent is a solid compound that is not reactive with lithium ions andcomprises solid-phase particles having a mean particle diameter of 10 nmto 5 μm.
 13. The integrated electrode assembly according to claim 12,wherein the solid compound comprises at least one selected from thegroup consisting of an oxide, a nitride, and a carbide that are notreactive with lithium ions.
 14. The integrated electrode assemblyaccording to claim 13, wherein the oxide that is not reactive withlithium ions comprises at least one selected from the group consistingof MgO, TiO₂ (rutile) and Al₂O₃.
 15. A method for preparing theintegrated electrode assembly according to claim 1, the methodcomprising: (1) homogenizing a linear polymer, monomers for across-linked polymer, a liquid-phase component comprising an ionic salt,a solid-phase component, and a polymerization initiator into a mixture;(2) coating the mixture on one electrode; (3) inducing polymerizationreaction through UV irradiation or heating to form a separation layer;and (4) placing a counter electrode on the separation layer, followed bypressing.
 16. A lithium secondary battery comprising the integratedelectrode assembly according to claim
 1. 17. A battery module comprisingthe lithium secondary battery according to claim 16 as a unit battery.18. A battery pack comprising the battery module according to claim 17.19. The battery pack according to claim 18, wherein the battery pack isused as a power source of a device.
 20. The battery pack according toclaim 19, wherein the device is an electric vehicle, a hybrid electricvehicle, a plug-in hybrid electric vehicle, or a power storage system.21. The integrated electrode assembly according to claim 2, wherein thepolymer matrix comprises an oxide-based non-cross-linked polymer,wherein the oxide-based non-cross-linked polymer comprises at least oneselected from the group consisting of poly(ethylene oxide),poly(propylene oxide), poly(oxymethylene), and poly(dimethylsiloxane),and wherein the polymer matrix comprises a polar non-cross-linkedpolymer, wherein the polar non-cross-linked polymer comprises at leastone selected from the group consisting of polyacrylonitrile, poly(methylmethacrylate), poly(vinyl chloride), poly(vinylidene fluoride),poly(vinylidenefluoride-co-hexafluoropropylene), poly(ethylene imine),and poly(p-phenylene terephthalamide).
 22. An integrated electrodeassembly comprising a cathode, an anode, and a separation layerintegrated between the cathode and the anode, the separation layercomprising 3 phases comprising: a liquid-phase component containing anionic salt, the liquid-phase component partially flowing from theseparation layer into the cathode and the anode of the integratedelectrode assembly and impregnates these electrodes to increase ionicconductivity of the cathode and the anode; a solid-phase componentsupporting the separation layer between the cathode and the anode; and apolymer matrix having affinity for the liquid-phase component andproviding binding force with the cathode and the anode, wherein thepolymer matrix is in the form of a mixture of linear polymer andcross-linked polymer, wherein the mixture of the linear polymer and thecross-linked polymer forms a viscoelastic structure, wherein theliquid-phase component is an electrolyte containing the ionic salt,wherein a weight ratio of the liquid-phase component to the polymermatrix is from 5:5 to 8:2, wherein the separation layer is in the formof single layer structure in which the solid-phase component and theliquid-phase component are incorporated in the polymer matrix, whereinthe linear polymer, the cross-linked polymer, the liquid-phasecomponent, and the solid-phase component are homogenized in theseparation layer, wherein a first surface of the separation layer formsa layer directly on a surface of the cathode and a second surface of theseparation layer forms a layer directly on a surface of the anode, andwherein the linear polymer partially permeates into the cross-linkedpolymer, and a size of the part of the linear polymer that permeatesinto the cross-linked polymer is 5 to 45% based on the total size of thelinear polymer.